1. Field of the Invention
This invention relates to polymerization processes and, in particular, to polymerization processes involving graft polymerization.
2. Art Background
Ziegler-Natta catalysis has been used extensively for producing many commercially significant polymers. Basically Ziegler-Natta catalysis involves the polymerization of an unsaturated monomer, e.g., an olefinic monomer, by the use of a Ziegler-Natta catalyst system including an organometallic such as an aluminum alkyl and a transition metal salt. (See, for example, John Boor, Jr., Ziegler-Natta Cataysis and Polymerizations, New York: Academic Press, 1979.)
Although many commercially viable polymers have been produced utilizing Ziegler-Natta catalysis, other polymers have engendered interest but have not exhibited all the properties desirable for a practical material. For example, acetylene and substituted acetylenes have been polymerized into polyacetylenes with a variety of catalyst systems. (See Boor supra, 540-543.) However, polyacetylene, the most significant of this class of polymers obtained through this polymerization, is essentially not soluble in any typical solvent. The insolubility of the polymer makes fabrication of devices such as solar cells utilizing this polyacetylene quite arduous. (See Weinberger et al, Applied Physics Letters, 38(7), 555 (1981) for a description of the fabrication procedure.) The polymer insolubility also severely limits control over the properties of the polyacetylene material ultimately used in devices. For example, there is essentially no control over the thickness and density of a polyacetylene layer formed as a component of a device such as a solar cell and no control over the interface between this polyacetylene component and the physically contacting components. Thus, even though typical Ziegler-Natta catalysis processes are quite useful for many applications, there are materials produced by Ziegler-Natta catalysis which have alluring properties but which have significant shortcomings.